In recent studies, human T cell lymphotropic virus (HTLV) type II has been found to be endemic in a number of indigenous New World Amerindian populations and the Wayuu and Tunebo Indians in Columbia, the Tobas and Matacos Indians in Argentina, and several pygmy populations in Africa, as well as within groups of injecting drug users (IUDs) and among patients attending sexually transmitted disease clinics. Epitope mapping analyses using synthetic peptides representing the RexII and TaxII proteins identified predominant seroreactivity to the carboxyl terminus of the HTLV-II G12 TaxII protein. This study showed that this active peptide can be used in immunoassays as a quick, simple serologic tool for assessing the minimal number of HTLV-IIb viruses present within specific populations, especially when genomic DNA is not available. Such information is useful for understanding the epidemiology and transmission of the various HTLV-II subtypes. Vescular stomatitis virus (VSV) replicates in the cytoplasm and causes rapid cytopathic effects. It was shown that following VSV infection, a nuclear factor that binds to a select set of interferon-stimulated responsive elements (ISRE) is induced in many cell types. This factor, VSV-induced binding protein (VIBP), was estimated to be 50 kDa and was distinct from known members of the interferon regulatory factor family known to bind to ISRE. The functional activity of VIBP was analyzed in cells stably transfected with the herpesvirus thymidine kinase-luciferase reporter gene that is under control of ISRE. While activity of the control promoter without ISRE was strongly inhibited following VSV infection (as a result of virus-mediated transcriptional shutdown of the host cell), the inhibition was reversed by the ISRE-containing promoter, which suggests that VSV infection, as a consequence of the induction of the VIBP gene differentially affects transcription of host genes. Evidence for developmental regulation of VIBP inducibility was obtained. Interferon consensus sequence binding protein (ICSBP) is a transcription factor of the IFN regulatory factor (IRF) family. Unlike other members of the family, ICSBP is expressed exclusively in the immune system. Immunoblot analysis was performed to study expression of ICSBP and other members of the family in various murine lymphocytes. The results show that all IRF family members are expressed constitutively in B cells throughout development. In contrast, ICSBP expression was undetectable in thymocytes and resting T cells while all other IRF proteins were detected in these cells. It was shown that the ICSBP expression in T cells is coupled with T cell activation that is partly due to IFN-gamma-induced Stat-1.